Press having automatic bend detector



Sept. 1, 1964 F. VAN ENDERT 3,146,819

PRESS HAVING AUTOMATIC BEND DETECTOR Filed Oct. 27, 1961 5 Sheets-Sheet 1 Fig.1

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3&1} Tum. im/ALFL United States Patent 3,146,819 PRESS HAVING AUTOMATIC BEND DETECTOR Fritz van Endert, Dusseldorf-Gberkassel, Germany, as- Signor to Waldemar Lindemann, Dusseldorf, Germany Filed Oct. 27, 1961, Ser. No. 148,225 Claims priority, application, Germany, Oct. 31, 1960, L 37,390 Claims. (Cl. 153-50) My invention relates to presses for bending sheet metal particularly for ship building purposes. Plates bent from sheet-metal for ship-building purposes are of such diverse shapes that they cannot be shaped by means of corresponding dies or jigs. Each sheet has therefore to be shaped by free cold bending, without subsequent calibration, on a press known as a shipbuilding press. Such presses comprise a punch for pressing the sheets over a localised area, e.g., a line or point area, and a co-acting bending block member provided opposite the punch with a pair of sheet-supporting ledges having opposing parallel edge parts which are laterally offset with respect to the punch axis and lie in a plane transverse to the punch axis.

The shaping of a sheet on known shipbuilding presses requires great care, attention and skill. The shaping of each sheet also requires a considerable amount of time, since each sheet is first rough shaped in a number of operations and then, with continual inspection, brought to the final shape by means of patterns in a further number of operations. For the magnitude of the punch stroke required at any time, the press operator has as a guide only the deviation of the sheet from the pattern, which he has to apply after each operation. From this deviation he has to estimate by feel how much further pressing is necessary. With this system, an error in estimation may always result in excessive pressing of the sheet. The correction then required is very complicated since the sheet has to be taken out of the press, turned around, re-inserted, and bent back.

The object of my invention is to provide a press which avoids the said difiicult, tedious and troublesome work. To this end, according to the invention, a detecting of gauging means is provided between the said edge parts of the ledges and opposite the punch which means follow, indicate and measure the bending of the sheet and stop the operative or working movement of the punch when the bending of a sheet has reached a desired value which is adjustable as required between any two pressing steps. The detecting means advantageously includes a piston member which is movable, against a biassing force, relative to the said edge parts when sheet is being bent, the detecting or gauging means stopping the operative movement of the punch when this piston member has been pushed relative to the edge parts through a predetermined but variable distance. Preferably the biasing force urges the piston member into a position in which its operative surface lies in the plane of said edge parts of the ledges.

In a press constructed according to my invention, the difficult work of pie-bending, application of the pattern, further bending, ire-application of the pattern, and particularly the danger of pressing the sheet to a greater degree than specified, is avoided and, on the basis of the data which can be immediately read from the working drawing of the plate to be formed or from the body plan, a program is prepared for adjustment of the values at which the detecting means stops the punch or reverses its movement at the end of each of the consecutive pressing steps. This may be effected completely automatically by means of a punched card made from the working drawing of the plate. This is accompanied by the considerable advantage of excluding the influence of fluctuations in the sheet thickness upon the resultant measurement supplied by the detecting means, and hence the measurement is independent of the sheet thickness.

After each pressing step the sheet springs back by a certain amount on the withdrawal of the punch, and this amount depends on the properties of the sheet material and the sheet thickness. If the amount of such springing back exceeds the curvature tolerance, this can be met by allowing the ram with the punch from the outset to have somewhat longer strokes than correspond directly to the desired degree of the bending. This need not, however, be done if, according to the preferred embodiment of the invention, the detecting means is used not only to indicate the bending of the sheets (i.e., the shape of the sheet as it is being bent), but also to measure the actual bend produced in the sheet. This is rendered possible by providing detecting or gauging means including a member which is movably mounted in a slide carrying the edge parts, both the detector member and the slide being movable in the direction of the punch movement against respective biassing forces tending to urge the detector member and the slide into respective predetermined positions so that the detector member and the slide move away from these positions during sheet bending but are able to move towards them in contact with the sheet on withdrawal of the punch. This ensures that the sheet bears against the detector member and the edge parts, even after withdrawal of the punch, so that the displacement of the detector member from its datum position with respect to the slide and its edge parts provides a direct indication of the bending produced. If this bending is insufiicient, as a result of a premature return movement of the punch the same can be operated again before the sheet is advanced, to correct the error, and this can again be effected automatically.

The said and other objects of my invention will be more fully understood from the following specification when read with the accompanying drawing in which an embodiment of my invention is illustrated. In the drawmg:

FIGURE 1 is a front view of a shipbuilding press of known construction to which the invention may be applied;

FIGURE 1a shows the outer end of the press ram with punch in side view in the direction of the arrow Ia in FIGURE 1;

FIGURE 2 shows on a larger-scale a cross-sectional view of the central operational part of a shipbuilding press as improved according to my invention;

FIGURE 3 is a top view in the direction of the arrow III in FIGURE 2;

FIGURE 4 is a sectional view on the line IV-IV in FIGURE 3;

FIGURE 5 is a cross sectional view corresponding to FIGURE 2 as appearing, during the bending of a sheet;

FIGURE 6 is a circuit diagram; and

FIGURES 7 and 8 show partially two views similar to FIGURE 5 to illustrate the arrangement for compensating the springing back of the sheet.

FIGURE 1 illustrates a press of known construction to which the present invention may be applied. The press comprises a frame 11, the top cross-member 12 of which carries the hydraulic drive 13 of a vertically movable ram 14. At the bottom end of the ram 14 is a punch 15, the operative surface 16 of which is formed by an elongated cylinder having a horizontal axis as is apparent from the side view shown in FIGURE 1a. Beneath the ram 14 the frame 11 carries a stand 17 on which is disposed a bending block member 18 adapted to support the sheet metal and to cooperate with the punch 15. The essential parts of the member 18 are two elongated ledges 19 having two laterally spaced parallel operating edge parts 20 situated in a horizontal plane on either side of the axis of the punch 15. Hydraulically extensible supports 21 are arranged on the right and left of the base 17.

A sheet B to be bent, which is shown in chain-dotted lines in FIGURE 1, is placed upon the edge parts 20 in such manner that one of its side edges is situated near one edge part 20 of the bending block member 18. In these conditions the left-hand support 21 is first retracted. The sheet may extend substantially beyond the length of the punch on either side of the drawing plane in FIGURE 1. By the descent of the punch 15 the sheet is gradually given the required curvature in a number of succeeding operations in the manner described in the introduction. In intermediate stage of sheet B shown in solid lines the part of the sheet situated on the right of the centre has already been bent. The supports 21 are always readjusted after one or more operations to protect those parts of the sheet which project considerably beyond the punch 15 against any undesired deformation. The conventional means for feeding the sheet into the press are not shown. If the length of the sheet exceeds the length of the punch, i.e., the length a. in FIG- URE 1a, the sheet is advanced not only laterally, but also in the longitudinal direction.

The press shown in FIGURES 2 to 4 is of the same type as that shown in FIGURE 1. Accordingly, a stationary bending block member having ledges 19 and edge portions 20 is arranged beneath the punch 15. The immovable ledges 19, however, are interrupted by a sliding block member 22 which is vertically displaceable in the stand 17 and is held in the raised position shown in FIG. 2 by springs 23. The displacement is limited at the top by strips 24 and at the bottom by the baseplate 25 of base 17. The springs 23 are subject to pre-stressing. At the top, the block member 22 has ledges 19a with edge portions 20a which fully correspond to the ledges 19 and edge portions 20 except that they are apart by the amount b by which the block member 22 can be pressed down against the springs 23. When the block member 22 is pressed down, the edge portions 20a of ledges 19a are aligned with the edge portions 20 of ledges 19.

A piston 26 is vertically slidable in the slidable block member 22 in line with the longitudinal axis AA of the ram 14. A prestress spring 27 tends to hold the piston in the position illustrated in FIG. 2, in which its head 28 lies with its operative face, i.e., the highest point 29 of its top part in the same plane as the edge portions 20a. A nut 30 is provided for adjustment purposes. An element in the form of lever 32 swingably mounted upon the sliding block member 22 at 31 is connected by a joint 33 to the piston 26 and by a link 34 to a sliding member 35 which is in turn connected to the movable part 36 of a potentiometer 37 provided with a sliding contact and mounted on the block member 22 so that the potentiometer is adjusted in accordance with relative movements between the pitson 26 and said member 22.

According to FIGURE 6, the potentiometer 37 forms one branch of a bridge, other branches of which consist of two fixed resistances 38 and another potentiometer 39. The inner diagonal of the bridge is formed by a current source 40. A highly sensitive polarised relay 41 is situated in the outer diagonal and in turn controls a magnetic valve 42 situated in the hydraulic circuit (not shown) of the drive 13. The polarised relay 41 adjusts the valve 42 when the current in the outer diagonal passes through zero. The position of the tapping of the potentiometer 37 at which this takes place depends upon the setting of the tapping of the potentiometer 39. The response of the relay 41 has the effect that the descending ram 14 is instantaneously stopped or reversed.

If a sheet B is worked upon as shown in FIGURE 5, the descending punch 15 will first press the slidable block member 22 downwardly from the position shown in FIG. 2 into the position shown in FIG. 5 wherein the edge parts 20 and 20a coincide and without any appreciable deformation of the sheet. As the sheet B then undergoes deformation at this stage, the piston 26 is pushed downwards against the spring 27 and the potentiometer 37 is displaced by a proportional amount constituting a measure of the amount of bending of the sheet B. When the potentiometer 37 reaches the position dependent upon the setting of the potentiometer 39, in which position the bridge is balanced, i.e., the current through the relay 41 passes through Zero, the downward movement of the ram 14 is stopped. At this moment the bending of the sheet B has reached the amount denoted by reference c in FIG- URE 5.

The working drawing of the plate to be formed from the sheet B will show what amounts of bending c have to e imparted to the sheet at certain distinct points or lines. This bending is adjusted at the potentiometer 39 between any two operations or series of operations. This may be effected by means of a punched card-controlled computer 43, which in turn moves the sliding contact of the potcntiometer To produce the punched card, it is only necessary to transfer the data of the working drawing to the punched card in conventional manner, which may be done very quickly. If, in addition, the sheet B is fed into the press automatically, the shaping of the sheet will not require any human action, apart from supervisory activity necessary for safety reasons.

When the ram M- is retracted, the plate B springs back by a certain amount. The actually achieved bending therefore deviates from the amount 0. If the springing back is so small that the sheet still remains in contact with the two edges 29 even after the withdrawal of the punch 15, the path of the piston 26 is an indication of the actual bending, which can therefore immediately be measured in a somewhat more advanced circuit. If the deviation of the actual bending from the desired bending exceeds the specified tolerance, the error can be obviated by moving the punch 15 down again, and this can in turn be effected automatically without difiiculty.

The sheet B after withdrawal of the punch 15 and after its springing back may, however, lose contact with the edge parts 26. As shown in FIGURE 7, the sheet will then rest only on the supports 21. The value at measured by the piston 26 is then less than the actual bending so that the measurement proves to be incorrect. This is averted by the sliding member 22 which according to FIGURE 8, is held with edge portions 20a against the sheet B by the springs 23 when the punch 15 is retracted, so that the piston 26 is displaced by the actual amount of bending although the sheet in view of its springing back has no longer any contact with the edge parts 20.

My press is also suitable for bending sheets for large tanks or containers in which the problems and conditions are very similar to those in shipbuilding. In this case it may be necessary to replace the above described elongated punch by a punch having a surface in the form of a segment of a sphere and the parallel edge portions 20 and 26a of ledges 19 and 19a by circular edge portions situated concentrically to the axis of the punch.

Although only one form of the invention has been shown and described by way of illustration, it will be understood that it may be constructed in various other embodiments which come within the scope of the appended claims.

I claim:

1. In a press for shaping metal sheets by cold bending the improvement comprising in combination (a) a ram with punching head reciprocable along its longitudinal vertical axis,

([1) a pair of stationary elongated bending members and an operating edge portion in each of said members, said edge portions located in opposing relation in a common horizontal plane receiving the metal sheet to be bent and symmetrically to said longitudinal axis of the ram;

(0) a gauge member substantially coaxial with the ram and extending with its upper end intermediate of said edge portions at least up to said horizontal plane, said gauge member mounted for reciprocable displacement in vertical direction;

(d) biasing means tending to hold the upper end of the gauge member at least at level with said horizontal plane and thus in permanent contact with the underside of the metal sheet; and

(e) control means operatively associated with the gauge member and adapted to stop the operational downward movement of the ram when the gauge member has been downwardly displaced by the bent in the metal sheet by a variably predetermined distance.

2. In a press for shaping metal sheets by cold bending the improvement comprising in combination (a) a ram with punching head reciprocable along its longitudinal vertical axis;

(b) a stationary block member with its upper surface facing said punching head;

(c) a pair of bending ledges on said upper surface and an operating edge portion in each ledge, said edge portions located in opposing relation in a common horizontal plane receiving the metal sheet to be bent and symmetrically to said longitudinal axis of the ram;

(d) a pistonlike gauge member substantially coaxial with the ram and extending with its upper end intermediate of said edge portions at least up to said horizontal plane, said gauge member reciprocably mounted in said block member;

(e) biasing means tending to hold the upper end of the gauge member at least at level with said horizontal plane and thus in permanent contact with the underside of the metal sheet; and

(f) control means operatively associated with the gauge member and adapted to stop the operational downward movement of the ram when the gauge member has been downwardly displaced by the bent in the metal sheet by a variably predetermined distance.

3. In a press for shaping metal sheets by cold bending the improvement comprising in combination (a) a ram with punching head reciprocable along its longitudinal vertical axis;

([2) a block member with its upper surface facing said punching head and finitely reciprocable in vertical direction toward and from said punching head between an uppermost and a lowermost position;

(0) a pair of bending ledges on said upper surface and an operating edge portion in each ledge, said ledge portions located in opposing relation in a common horizontal plane receiving the metal sheet to be bent and symmetrically to said longitudinal axis of the ram;

(d) first biasing means tending to hold the block member in its uppermost position;

(e) a pistonlike gauge member reciprocably mounted in said block member substantially coaxially with the axis of the ram and extending with its upper end intermediate of said edge portions at least up to said horizontal plane;

(3) second biasing means tending to hold the upper end of the gauge member at least at level with said horizontal plane and thus in permanent contact with the underside of the metal sheet; and

(g) control means operatively associated with the gauge member and adapted to stop the operational downward movement of the ram when the gauge member has been downwardly displaced by the bent in the metal sheet by a variably predetermined distance.

4. A press according to claim 3 wherein said control means comprise a potentiometer mounted on said block member and actuating means for said potentiometer operatively connecting the same with the gauge member and means electrically operated by the potentiometer to stop the operational downward movement of the ram when the gauge member has been downwardly displaced by the bent in the metal sheet by a variably predetermined dis tance.

5. In a press for shaping metal sheets by cold bending the improvement comprising in combination (a) a ram with punching head reciprocable along its longitudinal vertical axis;

(b) a slidable block member with its upper surface fac ing said punching head and finitely reciprocable in vertical direction toward and from said punching head between an uppermost and a lowermost position;

(c) a stationary frame block member slidingly supporting and guiding said reciprocable block member;

(d) a pair of first bending ledges on said upper sur face each including a first operating edge portion and located in opposing relation in a common horizontal plane receiving the metal sheet to be bent and symmetrically to said longitudinal axis of the ram;

(e) second bending ledges on said stationary frame block each having second operating edge portions located for alignment with said first operating edge portions;

(f) first biasing means tending to hold the slidable block member in its uppermost position with the first operating edges above the second operating edges;

(g) a pistonlike gauge member reciprocably mounted in said slidable block member substantially coaxially with the longitudinal axis of the ram and extending with its upper end at least up to said horizontal plane intermediate of said first operating edge portions;

(11) second biasing means tending to hold the upper end of the gauge member at least at level with said horizontal plane and thus in permanent contact with the underside of the metal sheet; and

(2') control means operatively associated with the gauge member and adapted to stop the operational downward movement of the ram when the gauge member has been downwardly displaced by the bent in the plate by a variably predetermined distance.

References Cited in the file of this patent UNITED STATES PATENTS 2,543,759 Cannon et a1 Mar. 6, 1951 2,797,724 Waldow July 2, 1957 2,840,135 Fowler June 24, 1958 FOREIGN PATENTS 163,769 Sweden July 1, 1958 1,038,514 Germany Sept. 11, 1958 

1. IN A PRESS FOR SHAPING METAL SHEETS BY COLD BENDING THE IMPROVEMENT COMPRISING IN COMBINATION (A) A RAM WITH PUNCHING HEAD RECIPROCABLE ALONG ITS LONGITUDINAL VERTICAL AXIS, (B) A PAIR OF STATIONARY ELONGATED BENDING MEMBERS AND AN OPERATING EDGE PORTION IN EACH OF SAID MEMBERS, SAID EDGE PORTIONS LOCATED IN OPPOSING RELATION IN A COMMON HORIZONTAL PLANE RECEIVING THE METAL SHEET TO BE BENT AND SYMMETRICALLY TO SAID LONGITUDINAL AXIS OF THE RAM; (C) A GAUGE MEMBER SUBSTANTIALLY COAXIAL WITH THE RAM AND EXTENDING WITH ITS UPPER END INTERMEDIATE OF SAID EDGE PORTIONS AT LEAST UP TO SAID HORIZONTAL PLANE, SAID GAUGE MEMBER MOUNTED FOR RECIPROCABLE DISPLACEMENT IN VERTICAL DIRECTION; (D) BIASING MEANS TENDING TO HOLD THE UPPER END OF THE GAUGE MEMBER AT LEAST AT LEVEL WITH SAID HORIZONTAL PLANE AND THUS IN PERMANENT CONTACT WITH THE UNDERSIDE OF THE METAL SHEET; AND (E) CONTROL MEANS OPERATIVELY ASSOCIATED WITH THE GAUGE MEMBER AND ADAPTED TO STOP THE OPERATIONAL DOWNWARD MOVEMENT OF THE RAM WHEN THE GAUGE MEMBER HAS BEEN DOWNWARDLY DISPLACED BY THE BENT IN THE METAL SHEET BY A VARIABLY PREDETERMINED DISTANCE. 